Systems for scrambling a television data stream are well-known in the art. One such system is described in the following U.S. Pat. No. 5,282,249 to Cohen et al.; U.S. Pat. No. 5,481,609 to Cohen et al. Scrambled television data streams described in the Cohen et al patents comprise both scrambled data representing television signals and coded control messages, also known as ECMs. The ECMs of Cohen et al comprise, in a coded form, data necessary for generating a control word (CW) which may be used to descramble the scrambled data representing television signals. An ECM is also termed a control word packet or CWP.
Data necessary for generating a control word is known in the prior art to take many different forms and may include, in general, at least any of the following: a control word; an encrypted control word packet which is intended to be decrypted before use; and a seed to a generating function such as, for example, a one-way function which generates the control word upon input of the seed. Throughout the present specification and claims the terms “control word generating information” and “CW generating information” are used interchangeably to designate data necessary for generating a control word in any appropriate form, as described above.
While the two patents to Cohen et al describe an analog system, that is, a system in which analog television data streams are broadcast to television sets, it is appreciated that similar ECM methods may also be used for digital television data streams. Generally, the scrambling techniques used for scrambling analog television signals such as, for example, the well-known “cut-and-rotate” technique, are chosen for their applicability to analog signals. In scrambling of digital television signals other scrambling techniques, well-known in the art, are used, the techniques being more appropriate to digital signals such as, for example, applying the well-known DES algorithm to the digital television signals.
Methods of transmitting a scrambled digital signal, including ECMs, are described in the MPEG-2 standard, ISO/IEC 13818-6, 12 Jul. 1996 and subsequent editions.
The system of Cohen et al and other systems described in the art share a feature of broadcasting an ECM synchronous to, generally immediately before or in a data stream parallel to, the actual scrambled broadcast. Typically, such an ECM is valid for a brief duration, with a new ECM being broadcast, in synchrony with a scrambled broadcast scrambled according to a new key, a few seconds, such as 10 seconds, after the broadcast of the previous ECM. Some systems have been described in which a key is sent, whether by broadcasting or by other means such as by mail, with a lower frequency, even as low as once a month. Such a system is described, for example, in U.S. Pat. Nos. 4,484,027 and Re 33,189 to Lee et al.
Patents describing systems related to encrypted broadcasting and/or key distribution in encrypted broadcasting systems include the following:
U.S. Pat. No. 4,228,321 to Flanagan describes a privacy transmission system with remote key control, in which key control signals are produced at the unscrambling location and are both used for unscrambling at that location and also transmitted to a scrambling location for use in scrambling.
U.S. Pat. No. 4,531,020 to Wechselberger et al describes a method for controlling the simultaneous broadcast of enciphered digital information signals, for example in a radio or television broadcast environment, to a plurality of subscribers using several levels of enciphering keys.
U.S. Pat. No. 4,531,021 to Bluestein et al describes enciphering digital information for transmission using a first key, common to all receivers, and a second key specific to one receiver of a small group of receivers.
U.S. Pat. No. 4,864,615 to Bennett et al describes a system for reproduction of secure keys by using distributed key generation data and a distributed encrypted prekey.
U.S. Pat. No. 4,866,770 to Seth-Smith et al describes a system for distributing video, audio, teletext, and data, in which system wide, individual decoder and group decoder control signals are transmitted as part of a composite signal. The group decoder control signal includes information relating to a group of decoders, while the individual decoder control signal includes information relating to the operation of individual decoders.
U.S. Pat. No. 4,944,006 to Citta et al describes a secure data packet transmission system utilizing a global encryption key as well as address keys for encrypting individually addressed bit packets.
U.S. Pat. No. 5,301,247 to Rasmussen et al describes a method for ensuring secure communications, in which two keys are combined together to produce a session key.
U.S. Pat. No. 5,499,298 to Narasimhalu et al describes a method for controlled dissemination of digital information, in which encrypted digital information is decrypted by a tamper-proof controlled information access device. Access to said tamper-proof controlled information access device is provided according to conditions specified by an information provider.
In general, methods of transmitting a scrambled digital signal, including ECMs, are well known. Some systems use a composite signal, that is, an analog or digital signal including a plurality of components. Typically the plurality of components includes both a scrambled television signal component and an ECM component, the ECM component comprising a plurality of ECMs. Prior art references which discuss examples of this type of signal include the following: DVB ETR289, “Digital Video Broadcasting (DVB): Support for use of scrambling and conditional access (CA) within digital broadcasting systems”; and DVB SIM061, “Technical specification of DVB-Simulcrypt”, 1 Apr. 1997.
Other documents relating to broadcasting of digital information include the DVB Specification for Data Broadcasting, document SI-DAT 360 (TM 1779), 12 Feb. 1997; and ATSC Digital Television Standard, document A54, October 1995 and subsequent editions.
Other methods of transmitting a scrambled digital signal, particularly useful in a case where the signal includes sub-signals encoded according to various different methods, are described in “Common Interface Specification for Conditional Access and other Digital Video Broadcasting Decoder Applications”, DVB document A017, May 1996 and subsequent editions; and in “Common Interface Specification for Conditional Access and other Digital Video Broadcasting Decoder Applications”, CENELEC EN50221:1997.
European Patent Application EP 0 375 539 to Guillon et al describes a process which includes access messages when emitting composite video signals, unscrambling the resulting signals using a smart card reader, whereby the smart card comprises encoded digital data, and utilizing an interactive process for the identification of a digital signature.
European Patent Application EP 0 461 029 to Jouet et al describes a transcontroller device that is intended for an installation conforming to a MAC/PACKET standard.
PCT Patent Application WO 99/45711 to Sered et al describes a key delivery method for use in an encoded communications system in which at least one encoded item including a first item encoded with a first item control word is sent in a communication stream from a sender to a receiver. The method described includes transmitting an item entitlement control message (IECM) comprising item control information, transmitting a stream entitlement control message (SECM) comprising stream control information, and combining at least part of the item control information and at least part of the stream control information to produce the first item control word.
U.S. Pat. No. 6,178,242 to Tsuria describes a digital recording protection system using ECMs.
The disclosure of U.S. Provisional Patent Application 60/206,056, from which the present application claims priority, is hereby incorporated herein by reference.
GB Patent 2 326 004 to Bauminger et al describes a viewer response method for use with an interactive telecommunications system. The method includes accumulating a user interaction history of a user of the system. The user interaction history includes user interaction information associated with a plurality of user interaction events; and provides user-sensible feedback, based at least in part on the user interaction history.
The disclosures of all references mentioned above and throughout the present specification are hereby incorporated herein by reference.
MPEG-4, the most recent edition of the MPEG standard, enables the broadcaster to manipulate video objects independently of each other. The MPEG-4 standard does not address the issue of conditional access at the level of objects.